1. Field of the Invention
This invention relates to a negatively-chargeable electrophotographic photosensitive member which may less cause image defects during image formation and can maintain good image formation over a long period of time, an image forming process making use of the negatively-chargeable electrophotographic photosensitive member, and an electrophotographic apparatus having such a negatively-chargeable electrophotographic photosensitive member. The negatively-chargeable electrophotographic photosensitive member is hereinafter also expressed simply as “electrophotographic photosensitive member”.
2. Description of the Related Art
Materials that form photoconductive layers in solid-state image pick-up devices, in electrophotographic photosensitive members in the field of image formation or in character readers are required to have properties as follows: They are highly sensitive and have a high SN ratio [photocurrent (Ip)/dark current (Id)]; have absorption spectral characteristics matched to spectral characteristics of electromagnetic waves to be radiated; have a high response to light and have the desired dark conductivity; and are harmless to human bodies when used.
Further, in the solid-state image pick-up devices, the materials are required to have properties that enable easy erasure of the afterimage in a prescribed time. In particular, in the case of electrophotographic photosensitive members of apparatus used as business machines in offices, the harmlessness in their use is an important point.
Materials that attract notice from such viewpoints include amorphous silicon (hereinafter also expressed as “a-Si”) whose dangling bonds have been modified with monovalent elements such as hydrogen atoms or halogen atoms, and its application to electrophotographic photosensitive members has been made.
Such electrophotographic photosensitive members making use of a-Si commonly include those in which an a-Si layer is formed on a conductive substrate (hereinafter also expressed as “a-Si photosensitive member”). As processes by which the a-Si layer is formed on the substrate, processes such as sputtering; thermal CVD, in which source gases are decomposed by heat; photo-assisted CVD, in which source gases are decomposed by light; and plasma-assisted CVD, in which source gases are decomposed by plasma are known in the art.
Of these, the plasma-assisted CVD (chemical vapor deposition), in which source gases are decomposed by direct-current or high-frequency or microwave glow discharge to form films on the substrate, has been put into practical use in a very advanced state in the production of electrophotographic photosensitive members.
Japanese Patent Application Laid-open No. 2002-236379 discloses a make-up in which, as layer configuration of an electrophotographic photosensitive member, a photoconductive layer composed chiefly of a-Si and containing a modification element added appropriately, and, in addition thereto, further provided on the surface side of the electrophotographic photosensitive member, an upper-part blocking layer having a blocking ability and a surface protective layer are deposited in layers.
The above Japanese Patent Application Laid-open No. 2002-236379 also discloses an electrophotographic photosensitive member provided between the photoconductive layer and the surface protective layer with an upper-part blocking layer which is provided with a region changing in content ratio of silicon atoms and carbon atoms and also containing a periodic-table Group 13 element in a prescribed state of distribution.
In addition, Japanese Patent Application Laid-open No. S57-177156 discloses a layer configuration in which a barrier layer provided between a substrate and a photoconductive layer for the purpose of reducing dark attenuation and residual potential is formed in a double layer.
The barrier layer formed in a double layer as disclosed in Japanese Patent Application Laid-open No. S57-177156 has layer configuration consisting of, from the substrate side;
a conductivity control type first barrier layer to which a periodic-table Group 13 element or a periodic-table Group 15 element has been added in the case of a positive-charging electrophotographic photosensitive member or in the case of a negatively-chargeable electrophotographic photosensitive member, respectively; and an electrically insulating type second barrier layer composed chiefly of silicon atoms and containing at least one kind of atoms selected from carbon atoms, nitrogen atoms and oxygen atoms.
Japanese Patent Application Laid-open No. H08-137119 also discloses an electrophotographic apparatus which has an a-Si photosensitive member, a developer having a toner with a small particle diameter and a two-component brush developing means in combination.
The electrophotographic apparatus disclosed in Japanese Patent Application Laid-open No. H08-137119 is an electrophotographic apparatus having; as the developer, a toner is used which is 1) 4.5 to 9.0 μm in weight average particle diameter and 2) 10 to 50 μC/g in triboelectric charge quantity; and as the electrophotographic photosensitive member, one at least being 5 or less in average of dielectric constants up to 1 μm in depth from the surface of the electrophotographic photosensitive member and/or having, in the range of 0.1 to 2 μm in depth from that surface, a region where an average of dielectric constants is 5 or less.